Abstract: A geomechanical model for the evolutionary process of lithospheric thinning in eastern China is constructed in light of the geological fact that significant changes took place in Cenozoic tectonics and geomorphology on the continent of China.Assuming that the various layers of the lithosphere are made of creep materials,the deep-level dynamic mechanism of synchronous basin-mountain coupling is quantitatively studied by using the numerical simulation method.A dynamic model of basin-mountain extension proposed by some geologists is theoretically discussed and verified.Study shows that lithospheric thickening or thinning is closely related to the thermal activity or thermal convection beneath the lithosphere and is one of the important factors affecting the formation of the synchronous basin-mountain coupling system.For the dynamic boundary condition of thermal convection of the basin-mountain system,only when both the upward buoyant force and the horizontal shear drag force caused by the thermal convection act on the bottom of the lithosphere,can the stress and strain conditions that accord with the actual tectonics and geomorphology be formed.Study of the creep features of the lithosphere shows that when the lasting forces act on the boundary,the stress and strain of various layers of the lithosphere vary with time.They increase rapidly in the initial stage and decrease steadily after reaching the peak value.The phenomenon of stress relaxation has great significance for the study of some common geological phenomena in tectonic activities.